1. Field of the Invention
The present invention relates to positioning devices and, more specifically, the present invention relates to a positioning device for optical communications systems.
2. Background Information
With the increasing popularity of wide area networks (WANs), such as the Internet and/or the World Wide Web, network growth and traffic has exploded in recent years. Network users continue to demand faster networks and more access for both businesses and consumers. As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.
An alternative to present day hardwired or fiber network solutions is the use of wireless optical communications. Wireless optical communications utilize point-to-point communications through free space and therefore do not require the routing of cables or fibers between locations. Thus, wireless optical communications are also known as free space or atmospheric optical communications. For instance, in a free space optical communication system, a beam of light is directed through free space from a transmitter at a first location to a receiver at a second location. Data or information is encoded into the beam of light, and therefore, the information is transmitted through free space from the first therefore, the information is transmitted through free space from the first location to the second location.
An important aspect of a free space optical communications system is tracking. In particular, it is important that the optical communications beam (e.g., laser beam) is aimed properly from the transmitter at the first location and that the receiver at the second location is aligned properly to receive the optical communications beam. For example, assume that a transmitter is mounted on a first building and that a receiver is mounted on a different second building. Assume further that there is a line of sight between the transmitter and receiver. It is important for the transmitter on the first building to be configured to accurately direct or aim the optical communications beam at the receiver on the second building.
Tracking is utilized for maintaining the alignment of the optical communications beam between the transmitter and receiver in various situations or disturbances. Examples of these various situations or disturbances include the swaying of the buildings due to for example windy conditions, vibration of the platforms on which the transmitter and/or receiver are mounted, atmosphere-induced beam steering, etc. If the tracking system is unable to compensate for disturbances, the optical communications beam is no longer properly aimed at the receiver and, consequently, communications between the transmitter and receiver are lost or impaired.
The present invention provides an apparatus and method for controlling a coordinate position and/or orientation of a stylus. The apparatus functions by positioning an armature to which the stylus is coupled. The armature is disposed within a magnetic fluid that causes the armature to be moved when the magnetic fluid is displaced by varying a magnetic field acting upon the magnetic fluid. In one implementation, the invention may be used in free space optical communication systems, wherein the stylus comprises the end portion of a fiber optic cable, and whereby positioning the end portion of the fiber optic cable enables the signal strength of both transmitted and received optical signals to be maximized.
According to a first aspect of the invention, the apparatus comprises a non-magnetic body that includes a cavity in which the magnetic fluid is held. A controllable active magnetic field-generating structure disposed in proximity to the cavity is used to generate the variable magnetic field that acts upon the magnetic fluid, causing it to be displaced, thereby enabling the armature to be moved to a desired coordinate position and/or orientation. In one embodiment, the controllable active magnetic field-generating structure comprises a plurality of electromagnetic stators disposed about the centerline of the cavity. Preferably, the apparatus also includes a static electromagnetic field-generating structure that is used to maintain the magnetic fluid within the cavity when the controllable active magnetic field-generating structure is disabled.
In one configuration, three electromagnetic stators are radially arrayed around the cavity with an angular displacement of approximately 120 degrees apart. In an alternative configuration, four electromagnetic stators are radially arrayed around the cavity with an angular displacement of approximately 90 degrees apart. Each of the electromagnetic stators includes a leading and trailing electromagnetic comprising a plurality of coils disposed about a pair of arms of a U-shaped magnetic core. Preferably, the ends of the arms are disposed to be in contact with the magnetic fluid and located such that they are disposed toward opposing ends of the armature. When the coils are supplied with current, various electromagnetic circuits are formed, wherein each magnetic circuit includes portions of the magnetic fluid. As a result, a controllable variable magnetic field is produced by controlling the currents supplied to the various electromagnets. The controllable variable magnetic field may then be used to move the armature to a desired position by displacement of the magnetic fluid. In addition, a tandem configuration is provided that enables both receiving and transmitting end portions of fiber optic cables to be positioned by a single device.
According to a second aspect of the invention, an integrated position sensor is built into the apparatus and is used to determine the position of the sensor. The position sensor comprises a plurality of electrodes radially disposed about a conductor that is disposed about a mid-portion of the armature. In one embodiment, the plurality of electrodes include a leading set of coplanar electrodes, and a trailing set of coplanar electrodes, wherein the leading set of electrodes is disposed toward one end of the conductor, and the trailing set of electrodes are disposed toward the opposite end. The magnetic fluid provides an electrical path between the electrodes and the conductor, wherein the resistance of the path is substantially proportional to the distance between a closest end of the conductor and each electrode. As a result, as the armature is displaced, the resistances change. By calculating the resistances, the position of the conductor, and thus the armature, can be determined.
According to another aspect of the invention, a servo control loop is provided that supports both an Acquire mode and a Tracking mode. In the Acquire mode, the armature can be moved to a desired coordinate position and/or orientation. In the tracking mode, a signal strength (i.e., energy level) corresponding to an optical signal transmitted from or received by the fiber optic cable is maintained at a maximum value by fine tuning the position of the end portion of the fiber optic cable based on a signal strength feedback signal.
According to still further aspects of the invention, a method is provided for positioning a stylus in accordance with the foregoing apparatus.